On the iOS platform, many of the optimizations you make for the Android mobile platform will be the same. Additionally, there are some extra bits regarding the iOS environment and its new native Metal graphic library.
Also, the graphic hardware on iOS devices is different, generally more advanced than the most of the Android models out there, and mount a PowerVR GPU which has really horse power to spare and with the latest Metal libraries become more powerful than ever. This is a reason for changing the textures import format. Luckily, when you switch platforms, Unity does this for you automatically.